Heating elements have wide applications in the construction, consumer and industrial sectors of the economy. Flat, longitudinally extended heating elements can be comprised of wire filaments or carbon fiber tows. Their physical characteristics such as thickness, shape, size, strength, flexibility and other features affect their applicability. Numerous types of thin and flexible heating elements have been proposed, for example U.S. Pat. Nos. 4,764,665 and 7,247,822. The '822 patent discloses a heating element assembly that uses a carbon fiber wherein the fibers are sandwiched between two layers of an “amorphous” polyester film. The heater element operates below 250.degree F. The technologies, such as the polyester film or the termination connector used in the creation of heating element products often limit the maximum operating temperatures before degradation, reliability, product life cycle and serviceability are affected. U.S. Pat. No. 7,662,002 discloses an assembly for connecting a tow of axially elongated carbon fibers with a plurality of discrete contact portions, referred to as a tow into a metal “U” shaped trough with knurled ridges. Manufacturing this type of connector requires pressing down a top male die with ridges to squeeze the carbon fiber layers and then uses ultrasonic welding to fix the fibers to contact points. A pneumatically activated carriage mechanism applies pressure to the preassembled parts. The '002 processes uses a 1000 watt ultrasonic welder producing a 20 kHz frequency and a long weld time of 600 milliseconds at 60 joules of energy.
The heating elements of the prior art have several problems that limit their usability. The first problem arises because the ultrasonic energy causes the carbon fibers to vibrate and some portion of them migrate beyond the sides of the polyester film causing shorts to ground when voltage is applied. The method of manufacture utilizing ultrasonic welding also slows down the manufacturing of the assembly. Additionally ultrasonic welding of carbon fibers to metal is unreliable when the connector temperature exceeds a temperature of 400F. For flat heating elements utilizing carbon fiber tows contained in a polyester sheath the temperatures cannot exceed a temperature of 350F. before the connector itself and the polyester suffer permanent damage. As will be described below, a novel sheathing material insofar as heater applications are concerned allows the temperature of the carbon fiber tow to exceed a temperature of 700F. and therefore the connector utilizing ultrasonic welding is unsuitable. Once the fibers are welded to the connector they become an integral part of the fiber tow preventing a complete substitution of the entire assembly in the event there is a malfunction in the field. What is needed is a connector that does not depend on ultrasonic welding and that is easily replaced in the field with out a complete replacement of the tow.